Wing tip device attachment apparatus and method

ABSTRACT

A wing tip device for attachment to a wing tip of a powered aircraft including: a first mounting formation, a second mounting formation spaced apart in a spanwise direction relative to the first mounting formation, a third mounting formation spaced apart in a chordwise direction relative to the first and second mounting formations, wherein each of the first, second and third mounting formations are configured for attachment to at least one of a wing spar and a wing rib, and, at least one of the mounting formations is configured to permit movement of a portion of the wing tip device in the spanwise direction relative to a portion of the wing tip.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/317,784 filed Oct. 28, 2011, and claims priority to GB ApplicationNo. 1018185.7, filed 28 Oct. 2010, the entire contents of theseapplications are incorporated by reference.

BACKGROUND

The present invention is concerned with wing tip device attachmentapparatus and method. More particularly, the present invention isconcerned with an apparatus and method for attaching a wing tip devicesuch as a winglet to the tip of a passenger aircraft wing.

Wing tip devices are well known in the art. Devices such as winglets,raked wing tips and fences are collectively known as aerodynamic wingtip devices and are used to reduce the effects of lift induced drag.

Lift induced drag is caused by the generation of vortices at the wingtip. Such drag is mitigated by an increase in wing span. Increases inwing span in the plane of the wing are not always possible due to spacerequirements at, e.g. airports. As such out-of-plane extensions to thewing are commonly used to increase the effective wing span withoutincreasing the geometric span of the aircraft. These take the form ofaerodynamic wing tip devices.

There is an ever increasing drive to increase the efficiency ofpassenger aircraft. One way to achieve increased efficiency is toincrease the size of the aerodynamic wing tip device. Typical ratios ofwinglet span to the thickness of the wing tip at the attachment point(wingbox thickness) are commonly above 10 and may be as high as 12 to 15in modern passenger aircraft. Because the thickness of the wing is lowat the tip, the vertical moment arm available to react to the loadsgenerated by the wing tip device under both its own weight and underaerodynamic forces is low. Therefore, the forces and stresses generatedin this area are high.

Other wing tip devices include external tanks, refueling pods etc whoseprimary purpose is not to improve the aerodynamic efficiency of thewing, but nerveless are attached to, and produce a force on, the wingtip.

Known wing tip devices are generally attached in one of two manners. Thefirst is to use a series of splice plates or butt straps which span theupper and lower skins of the wing tip device and the wingbox at thepoint at which they join.

The second method is to use abutting plates joined by tension bolts.

Disadvantageously, both of these methods only utilise a very smallmoment arm to react the loads. The splice plates transfer load throughthe wing skin, which is primarily designed to absorb the bending loadacross the wing span, and less well suited to absorb local,concentrated, loads. As such, the large local load introduced into thewing skin requires structural reinforcement. The additional weight thiscauses is undesirable.

Further, because the wing skin is not particularly strong, many joininglocations are required to spread the applied load. Although this has thedesired effect of reducing the load per joining location, it creates astatically indeterminate system making the loads at each point difficultto predict. Therefore each joint is typically over-engineered addingweight and cost to the aircraft.

Cyclic loading is common in aircraft. This introduces additionalstructural requirements, in particular to the tension bolt design. Inorder to mitigate the effects of fatigue, the bolts have to bepre-tensioned with an interference fit. This is undesirable as it addscomplexity to the manufacturing process, and makes maintenance andreplacement more difficult

A still further problem with the above two methods is that because ofthe heavy bolting and large surface area of contact between the variouscomponents in both methods, the interface between the parts is quitesensitive to differences in geometry at the interface. As such, anymis-match between the two components needs to be addressed with fettlingupon assembly. This increases the cost of assembly and makes it moredifficult to replace the wing tip devices in service.

Further, temperature effects and loading in use can cause differentialexpansion/contraction of the wing tip device and the wing tip, which cancause high stresses at the mounting points.

SUMMARY OF INVENTION

It is an aim of the present invention to overcome or at least mitigateone or more of the above problems.

According to a first aspect of the invention there is provided a wingtip device for attachment to a wing tip of a powered aircraft, the wingtip device comprising: a first mounting formation, a second mountingformation spaced apart in a spanwise direction relative to the firstmounting formation, a third mounting formation spaced apart in achordwise direction relative to the first and second mountingformations, wherein each of the first, second and third mountingformations are configured for attachment to at least one of a wing sparand a wing rib, and, at least one of the mounting formations isconfigured so that relative movement in the spanwise direction of thewing tip device to a wing tip is permitted in use.

Advantageously, thermally induced spanwise relative expansions andcontractions between the wing tip device and wing tip do not causeexcessive stresses because of the relative movement permittedtherebetween. Similarly, relative movement resulting from flexing of thewings is permitted without causing significant stresses.

Further, by designing the system such that certain attachment points arenot required to react the incident forces, they can be designed as such,increasing the predictability of force magnitude on the other attachmentpoints, and moving the system towards static determinancy.

Preferably the mounting formations are arranged such that relativemovement is permitted at least two of the mounting formations to providea statically determinate loading system. More preferably another of themounting formations is configured so that relative movement in thechordwise direction of the wing tip device to the wing tip is permitted,and still another of the mounting formations is configured so thatrelative movement in the vertical direction of the wing tip device tothe wing tip is permitted.

Wing spars are load-bearing components and if constructed fromcomposite, also tend to be over-engineered (i.e. thicker than necessary)in the region of the wing tip because they are not easily tapered fromthe fuselage.

The present invention utilises this material to react the loads from thewinglet. Further, the rear spar extends across the entire span of thewing, and as such a large moment arm can be incorporated into the designto reduce the local loads and stresses.

Still further, given the mounting formation arrangement prescribes astatically determinate assembly, it will be known what loads (type andmagnitude) will be felt where, thus meaning that the structures can bemore efficiently engineered, without the need to account foruncertainties in the amount of load reacted by a given component.

According to a second aspect of the invention there is provided a wingtip device for a powered aircraft comprising a mounting member extendingfrom the wing tip, the first mounting member defining a first attachmentformation comprising a first pivotable joint means for rotation about afirst axis at a first position proximate the wing tip device, anddefining a second attachment formation distal to the wing tip device.

Such a structure permits rotation of the wing tip device into positionabout the first pivotable joint means and subsequent attachment at thesecond attachment point. It will be noted that by “pivotable jointmeans” we mean, inter alia, a pivot shaft, pivot bore or pivot assembly.

According to a third aspect of the invention there is provided a methodof assembling a wing tip device to a wing of a powered aircraftcomprising the steps of providing a wing tip, providing a wing tipdevice, pivotably attaching the wing tip device to the wing at a firstposition, pivoting the wing tip device about the first position,attaching the wing tip device to the wing at a second position spacedfrom the first position.

Advantageously, the method permits easy installation of wing tip devicesupon assembly and in service.

According to a fourth aspect of the invention there is provided anaircraft wing subassembly comprising a wing skin defining a first outersurface, and a structural reinforcement member within the wing, thestructural reinforcement member defining a second outer surface, whichstructural reinforcement member is arranged within the wing such thatthe first outer surface and the second outer surface form part of anouter wing surface.

Advantageously, by using the reinforcement as part of the wing skin, thereinforcement can be made as large as possible, thus providing maximumresistance to bending moments.

SUMMARY OF DRAWINGS

A wing tip device attachment apparatus and method in accordance with theinvention will now be described by way of example and with reference tothe accompanying figures in which:

FIG. 1 is a front view of a wing tip and wing tip device;

FIG. 2 is a free body diagram of a part of the wing tip and wing tipdevice of FIG. 1;

FIG. 3a is a view of a wing tip device and mounting apparatus inaccordance with the present invention;

FIG. 3b is a schematic view of the wing tip device and mountingapparatus of FIG. 3 a;

FIG. 4a is a perspective view of a first constraint type;

FIG. 4b is a perspective view of a second constraint type;

FIG. 4c is a perspective view of a third constraint type;

FIG. 4d is a perspective view of a fourth constraint type;

FIGS. 5a to 5f are schematic plan views of various reaction loadsexhibited by the mounting apparatus of FIG. 3;

FIGS. 6a to 6d are front schematic views of an attachment method of awing tip device according to the present invention;

FIG. 7 is a perspective view of a second wing tip device in accordancewith the present invention;

FIG. 8a is a chordwise cross-section view of a wing tip fitted with thewing tip device of FIG. 7; and

FIG. 8b is a close-up view of a part of the wing tip device of FIG. 7shown in plan section view.

DETAILED DESCRIPTION OF INVENTION

Referring to FIG. 1, a wing assembly 100 comprises a wing tip 102(formed by the end of a wing) and a wing tip device 104. In this examplethe wing tip device 104 is a winglet. The wing tip 102 terminates at anoutboard end 106 with thickness Tw. This area is also known as thewingbox. The wing tip device 104 extends from the outboard end 106 andhas a winglet span Sw1. Turning to FIG. 2, the wing tip device 104experiences an aerodynamic lift force Fw1 which acts through its centreof pressure 108 generally towards the aircraft fuselage (not shown).

The wing tip device 104 is attached to the wing tip 102 at the outboardend 106. As such a torque, Tw1, is generated which is a product of thewinglet force Fw1 and the perpendicular distance Lw1 to the centre ofthe outboard end 106 of the wing tip 102 (also known as the wingletmoment arm).

In order to keep the wing tip device 104 stably attached to the outboardend 106 of the wing tip 102, the torque Tw1 created by the winglet forceFw1 must be reacted at the outboard end 106. Because the moment armavailable at the outboard end 106 can only be as high as the wingboxthickness Tw, the reaction forces Fw1, Fw2 are extremely high. As suchthe material in the area of the outboard end 106 of the wing tip 102 hasto be reinforced adding weight and complexity to the aircraft.

As mentioned above, known attachment methods include splice plates whichspan the upper and lower skin of the wing tip device 104 and the wingtip 102. Alternatively abutting perpendicular plates at the outboard end106 which are used and held in position by tension bolts. In both casesa moment arm defined vertically between the two wing covers is used toreact the forces.

Turning to FIGS. 3a and 3b , a wing assembly 110 is shown comprising awing tip 112 and a winglet 114. The wing tip 112 comprises a front spar116 and a rear spar 118, both running in a spanwise direction andconverging along the span of the wing towards the wing tip. A series ofribs 120 are positioned along the wing span and extend in the directionof the wing chord. A wing tip end 122 is provided at the end of the wingtip. The spars and ribs are covered by a wing skin 124 primarilydesigned to present an aerodynamic surface to the airflow. The wing tip112 terminates at an outboard end 126.

The winglet 114 comprises a winglet root 128 and a free end 130distanced from and vertically spaced from the winglet root 128.

A main beam 132 extends from a position partway between the free end 130and the winglet root 128 and extends towards the winglet root 128 andbeyond into the wing tip 112 as will be described below. The main beam132 is spaced towards the rear of the winglet 114. A canted spar 134runs from the position midway along the winglet 114 towards the wingletroot 128 but diverges from the main beam 132 towards the forward part ofthe winglet 114. The canted spar 134 extends into the wing tip 112 aswill be described below.

The main beam 132 and the canted spar 134 are supported by a number ofwinglet ribs 136 which extend chordwise within the winglet 114. Awinglet skin 138 covers the winglet in order to present an aerodynamicsurface to the airflow.

Referring to FIG. 3b , the wing assembly 110 is shown in schematic form.The main beam 132 extends from the winglet 114 into the wingbox of thewing tip 112 to be generally parallel and adjacent to a forward face ofthe rear spar 118. The main beam 132 is attached to the rear spar 118 attwo positions; position B proximate the first rib 120 and position Aproximate the wing end rib 122. It will be noted that A and B are spacedapart and, in particular, spaced apart by a distance which is largerthan the thickness of the wingbox Tw.

The canted spar 134 also extends into the wing tip 112, but in thisexample is only arranged to abut the wing tip rib 122 and is attachedthereto at point C.

A, B and C are therefore first, second and third mounting formations,and will be described in greater detail below.

Turning to FIGS. 4a to 4d , various examples of attachment methods areshown. FIG. 4a shows the main beam 132 attached to the outermost rib 120via a spigot joint 140.

FIG. 4b shows the main beam 132 attached to the rear spar 118 via asingle lap shear joint 142.

FIG. 4c shows a main beam 132 passing through the wing tip rib 122 andattached to the rear spar 118 and a sub-spar 144 extending from the wingtip rib 122 via a double lap shear joint 146.

FIG. 4d is a plan view of a canted spar 134 attached to the front spar116 via a web in single lap shear

In the examples shown in FIG. 3b , the attachment at B is a spigot jointper FIG. 4a , the attachment at A is a double lap shear joint as shownin FIG. 4c and the attachment at C is a locking pin.

Referring to FIGS. 5a to 5f , reaction of the various loads and momentswill be described. In all cases the co-ordinate system used is X in apositive spanwise direction, Y in a fore aft (chordwise) direction and Zin the vertical direction.

Referring to FIG. 5a , the bending moment MY (the tendency of the tip ofthe wing tip device to move towards the fuselage) is reacted atattachment points A and B as shown. This is the type of bending momentproduced by the winglet lift force Fw1, and as shown it is reacted overa large moment arm (the distance from A to B), reducing the force, andhence stress levels.

Referring to FIG. 5b , the moment MZ (mainly resulting from drag) isreacted where the winglet abuts the wing tip at the trailing edgeproximate the attachment point A and at the connection at point C whichis held in direction X.

Referring to FIG. 5c , the torsion MX is reacted by the fact thatattachment points A and C are constrained in the vertical direction(i.e. in direction Z).

Referring to FIG. 5d , FY (drag force) is reacted primarily atattachment point C.

Referring to FIG. 5e , FZ (lift) is reacted at points A and C.

Finally, referring to FIG. 5f , the side force FX is reacted at points Aand C.

The release of certain degrees of freedom (e.g. the inability of thespigot at B to react the side force FX) allows the system some relativemovement to avoid thermally induced stresses whilst making the loadsmore predictable (moving towards a statically determinate system). Forexample, because the joint at point B does not need to react the sideforce, it can be made smaller as a result (i.e. can be optimised for amore predictable load case).

It will be noted that because the present invention only uses threeattachment points, it is possible to constrain the winglet 114 in amanner which makes the system statically determinate. Therefore, eachattachment point can be designed around a known load case. This offersan advantage over the prior art in which generally a high number offixings are used for load-bearing purposes and consequently a staticallyindeterminate system is formed in which the exact load case on eachattachment point is unknown. Therefore each attachment point has to beover-engineered to cope with the worst possible case.

Referring to FIGS. 6a to 6d , a method of attachment of a wing tipdevice is shown. A wing assembly 200 is shown comprising a wing tip 202and a winglet 204. The winglet 204 is attached to the wing tip 202 in asimilar manner to the wing assembly 110. In the wing assembly 200, theattachment points A and C have their horizontal chordwise axes (parallelto axis Y) of rotation aligned as will be described below. The winglet204 is moved proximate the wing tip 202 on a trolley jack or similar asshown in FIG. 6a . The jack 206 is elevated to move the winglet 204 suchthat the attachment points A, C are aligned with their respectivereceiving formations on the wing tip 202. The joints can then beassembled such that the winglet 204 can be rotated above the axis Y atthe attachment points A, C from the position shown in FIG. 6B to theposition shown in FIG. 6C. The winglet 204 is rotated into place and theattachment point B is secured in order to prevent any rotation of thewinglet 204 relative to the wing tip 202. The jack 206 can then beremoved, as shown in FIG. 6 d.

This method of assembly demands an interruption in the skin on the topof the wing tip 202. This can be achieved by making the winglet meanbeam part of the aerodynamic surface of the wing (see below) orproviding a replaceable panel in the wing skin. The method permitsreplacement of the winglet in-field without the need for an overheadcrane and/or hanger space.

Referring now to FIG. 7, a wing assembly 300 is shown comprising a wingtip 302 and a winglet 304.

The wing tip 302 comprises a front spar 306 and a rear spar 308. A frontspar 306 comprises two flanges extending in a chordwise direction; anupper flange 310 and a lower flange (not visible). The flanges extendtowards the rear spar 308. Similarly, the rear spar 308 comprises anupper flange 312 and a lower flange 314 both of which extend towards thefront spar 306. A rib 316 extends between the spars 306, 308 in achordwise direction at the widest parts of the flanges 310, 312, 314.

The winglet 304 comprises a flat main beam 318 which extendssubstantially parallel to the skin of the winglet 304. The main beam 318tapers from a point midway along the winglet 304 to its thickestcross-section at a mid-point 320 at the position where the winglet andthe wing tip meet and tapers inwardly again at attachment point 322within the wing tip 302.

The beam 318 is attached to the wing tip 302 via a spigot at point B, alap shear joint at point A and a further lap shear joint at point C. Theaxes of rotation of the lap joints at A and C are aligned such that thewinglet 304 can be assembled to the wing tip 302 in a similar manner asdescribed in FIGS. 6a to 6 d.

It will be noted that the beam 318 tapers from the point of maximumbending moment at area 320 to areas of lower bending moment at itsopposite ends within both the winglet 304 and the wing tip 312.Referring to FIG. 8a , a section is shown through the wingbox of thewing tip 302 proximate points A and C. It will be noted that the mainbeam 308 is designed to form part of the aerodynamic surface of thewing. Referring to FIG. 8b , the skin of the wing tip 302 istransitioned to the main beam 318 by use of flexible skin panels 324which define a tapered region 326 to allow transition to the surface ofthe beam 318. In this way, the beam 318 can be as large as possible inorder to provide as much area for reaction on the various loads andstresses it undergoes.

It will also be noted that by making the beam 318 part of the wing skin,the assembly process as shown in FIGS. 6a to 6d is made easier as theskin of the wing tip 302 does not need to be replaced over the beam 318.

Variations fall within the scope of the present invention.

The invention claimed is:
 1. A wing tip device for attachment to a wingtip of a powered aircraft, the wing tip device comprising: a firstmounting formation, a second mounting formation spaced apart in aspanwise direction relative to the first mounting formation, a thirdmounting formation spaced apart in a chordwise direction relative to thefirst and second mounting formations, wherein each of the first, secondand third mounting formations are configured for attachment to at leastone of a wing spar and a wing rib, and, at least one of the mountingformations is configured to permit movement of a portion of the wing tipdevice in the spanwise direction relative to a portion of the wing tip.2. The wing tip device according to claim 1 wherein the wing tip devicecomprises a first load-bearing structure that extends from the wing tipdevice into the wing tip and the first load-bearing structure comprisesthe first mounting formation.
 3. The wing tip device according to claim2 wherein the first load-bearing structure comprises the second mountingformation.
 4. The wing tip device according to claim 2 wherein the firstload-bearing structure comprises a beam.
 5. The wing tip deviceaccording to claim 1 wherein the wing tip device comprises a secondload-bearing structure that comprises the third mounting formation. 6.The wing tip device according to claim 5 wherein the second load-bearingstructure comprises a beam.
 7. The wing tip device according to claim 1,in which the first and second mounting formations are aligned in aspanwise direction.
 8. The wing tip device according to claim 1 in whichthe first and third mounting formations are aligned in a chordwisedirection.
 9. The wing tip device according to claim 6, in which thefirst and third mounting formations comprise a pivotable joint.
 10. Awing assembly for a powered aircraft, the wing assembly comprising awing and a wing tip device attached to a tip of the wing, wherein thewing tip device comprises: a first mounting formation, a second mountingformation spaced apart in a spanwise direction relative to the firstmounting formation, a third mounting formation spaced apart in achordwise direction relative to the first and second mountingformations, wherein each of the first, second and third mountingformations is attached to at least one of a spar of the wing and a ribof the wing, and, at least one of the mounting formations permitsmovement of a portion of the wing tip device in the spanwise directionrelative to a portion of the wing tip.
 11. The wing assembly accordingto claim 10 wherein the wing tip device comprises a first load-bearingstructure that extends from the wing tip device into the wing tip andthe first load-bearing structure comprises the first mounting formation.12. The wing assembly according to claim 11 wherein the firstload-bearing structure comprises the second mounting formation.
 13. Thewing assembly according to claim 10, wherein the first load-bearingstructure comprises a beam.
 14. The wing assembly according to claim 10wherein the wing tip device comprises a second load-bearing structurethat comprises the third mounting formation.
 15. The wing assemblyaccording to claim 14 wherein the second load-bearing structurecomprises a beam.
 16. The wing assembly according to claim 10 whereinthe second mounting formation permits movement of a portion of the wingtip device in the spanwise direction relative to a portion of the wingtip.
 17. The wing assembly according to claim 16 wherein the firstmounting formation is proximal the tip of the wing and the secondmounting formation is distal to the tip of the wing.
 18. The wingassembly according to claim 10 wherein at least one of the first, secondand third mounting formations is attached to at least one of a spar ofthe wing and a rib of the wing such that a portion of the wing tipdevice is retained in the spanwise direction relative to a portion ofthe wing tip.
 19. The wing assembly according to claim 18 wherein atleast one of the first, second and third mounting formations is attachedto at least one of a spar of the wing and a rib of the wing such that aportion of the wing tip device is substantially fixed in the spanwisedirection relative to a portion of the wing tip.
 20. The wing assemblyaccording to claim 18 wherein the third mounting formation is attachedto at least one of a spar of the wing and a rib of the wing such that aportion of the wing tip device is retained in the spanwise directionrelative to a portion of the wing tip.
 21. The wing assembly accordingto claim 20 wherein the third mounting formation is attached to at leastone of a spar of the wing and a rib of the wing such that a portion ofthe wing tip device is substantially fixed in the spanwise directionrelative to a portion of the wing tip.
 22. The wing assembly accordingto claim 20 wherein the third mounting formation is provided proximalthe leading edge of wing tip and the first mounting formation isprovided distal to the leading edge of the wing tip.
 23. The wingassembly according to claim 10 wherein at least one of the first, secondand third mounting formations is attached to at least one of a spar ofthe wing and a rib of the wing such that a portion of the wing tipdevice is retained in the vertical direction relative to a portion ofthe wing tip.
 24. The wing assembly according to claim 23 wherein atleast one of the first, second and third mounting formations is attachedto at least one of a spar of the wing and a rib of the wing such that aportion of the wing tip device is substantially fixed in the verticaldirection relative to a portion of the wing tip.
 25. The wing assemblyaccording to claim 23 wherein the first and third formations are eachattached to at least one of a spar of the wing and a rib of the wingsuch that a portion of the wing tip device is retained in the verticaldirection relative to a portion of the wing tip.
 26. The wing assemblyaccording to claim 25 wherein the first and third formations are eachattached to at least one of a spar of the wing and a rib of the wingsuch that a portion of the wing tip device is substantially fixed in thevertical direction relative to a portion of the wing tip.
 27. The wingassembly according to claim 10 wherein the first attachment formation isattached to a first spar of the wing, the second attachment formation isattached to a rib of the wing and the third attachment formation isattached to a second spar of the wing that is spaced, in the chord-wisedirection, from the first spar of the wing.
 28. The wing assemblyaccording to claim 10 wherein the wing comprises first, second and thirdcomplimentary mounting formations and the first, second and thirdmounting formations of the wing tip device cooperate with the first,second and third complimentary mounting formations of the wing to formfirst, second and third attachments respectively, wherein at least oneof the attachments permits movement of a portion of the wing tip devicein the spanwise direction relative to a portion of the wing tip.
 29. Thewing assembly according to claim 10 wherein each of the first, secondand third formations comprises a protrusion or defines a space forreceiving a protrusion.
 30. The wing assembly according to claim 10wherein the first and second mounting formations are aligned in aspanwise direction.
 31. The wing assembly according to claim 10 whereinthe first and third mounting formations are aligned in a chordwisedirection.
 32. The wing assembly according to claim 10 wherein the firstand third mounting formations comprise a pivotable joint.